1. Field of the Invention
The present invention relates to a radiation diagnosis apparatus capable of indicating a center of radiation visual field.
2. Description of the Prior Art
Conventionally, there has been a radiation diagnosis apparatus wherein radiation (radiant ray) is irradiated to a subject (a person to be diagnosed) placed on a bed, and then the radiation passed through the subject is converted into an electric signal by an I.I (image intensifier) etc. to be displayed on a display apparatus. As such radiation diagnosis apparatus, an over table tube type (referred to as "over type" hereinafter) radiation diagnosis apparatus in which the radiation is irradiated to the subject from the upper side of the subject, and an under table tube type (referred to as "under type" hereinafter) radiation diagnosis apparatus in which the radiation is irradiated to the subject from the lower side of the subject have been well known in the art.
The over type radiation diagnosis apparatus has no intervening body between a field stop apparatus and the subject, whereas the under type radiation diagnosis apparatus has an intervening body such as a top plate of a housing between the field stop apparatus and the subject because of its structure. When the subject is diagnosed actually, either the over type radiation diagnosis apparatus or under type radiation diagnosis apparatus can be selected according to the contents of required diagnosis.
However, in the over type radiation diagnosis apparatus, an irradiation displaying apparatus for indicating a center of an irradiation visual field is attached to the field stop apparatus. Thus, the operator of the diagnosis apparatus can recognize the center of the irradiation visual field indicated by the irradiation displaying apparatus when the radiation is irradiated to the subject. On the other hand, since, in the under type radiation diagnosis apparatus, there exists the intervening body between the field stop apparatus and the subject, the center of the irradiation visual field could not be indicated in the same manner as in the over type radiation diagnosis apparatus.
Therefore, in case an arm of a child as the subject must be diagnosed by the under type radiation diagnosis apparatus, for instance, there have been caused some drawbacks such that the irradiation of the radiation is effected under the condition wherein the arm of the subject is not placed within the irradiation visual field.